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Old Mar 14th 2017, 03:29 PM   #1
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Physical chemistry - nernst equilibrium potential

Hey you all!

I am taking a neuroscience class and am struggling with the Nernst equation.

I am doing something wrong, because I never seem to get the answer right.

Here is the question, and sorry if I am posting this in the wrong threads:

Calculate the reversal potential of a calcium selective conductance at 37 Celsius if the intracellular calcium concentration is 1 uM and the extracellular calcium concentration is 2 mM.

I am assuming I have to convert 1 uM to mM... would be 2000 mm?

I have tried this:

E CA +2 : RT over ZF x IN (Ca+ 2 over 1)

= 8.314 Joules over +2 times 310.15 over 96.500

I keep getting wrong numbers when calculating:

The multiple choice answers are as follows:

1. - 90 mV

2. - 103.5 mV

3. 101.5 mV

4. 203.0 mV


My guess is -103.5, but I don't just want to be guessing. I want to know how to do the equation properly and how to get the correct answer.


PLEASE HELP?!

THANK YOU!!
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Old Mar 14th 2017, 04:02 PM   #2
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You have the unit conversion the wrong way round.

1 millimole = 1000 micromoles.

Are you also using absolute temperature for T, not degrees Celsius?
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Old Mar 15th 2017, 04:10 PM   #3
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Hey, thanks for the reply!!

Oh wow, i had no idea I had the conversion wrong. thanks for that. So, if 1 = 1000 mm , would i have to convert the 2mm?

I did convert Celsius to Kelvin. 37 = 310.15K
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